In process control carried out at a chemical plant and so forth, use is made of a measuring system driven by, for example, a built-in thionyl chloride based primary cell for measurement of process parameters (pressure, temperature, flow rate, and so forth) of a fluid under test. The measuring system is described hereinafter with reference to a block diagram of FIG. 6.
In FIG. 6, a measuring system 10 comprises a thionyl chloride based primary cell 1, and an internal circuit 9. The internal circuit 9 is comprised of a constant voltage circuit unit 2, a connection controller 3, a control operation unit 4, a communication unit 5 for executing radio communication or wire communication, a first connector 6a, a second connector 6b, a first circuit block 7a, a second circuit block 7b, and a cell voltage measurement unit 8.
An anode (an output) of the thionyl chloride based primary cell 1 is connected to an input of the constant voltage circuit unit 2 as well as the cell voltage measurement unit 8 while a cathode thereof is connected to a common voltage GD.
The constant voltage circuit unit 2 converts an output voltage of the thionyl chloride based primary cell 1 into a predetermined voltage (for example, 3.3 V) to be subsequently outputted. An output of the constant voltage circuit unit 2 is connected to the connection controller 3, the control operation unit 4, the communication unit 5, the first connector 6a, and the second connector 6b, respectively, as a power source thereof, respectively, the output of the constant voltage circuit unit 2 being further connected to the first circuit block 7a via the first connector 6a, and to the second circuit block 7b via the second connector 6b, as a power source thereof, respectively.
The first circuit block 7a is provided with a display unit made up of liquid crystals and so forth, for displaying measured values, and the second circuit block 7b is provided with a sensor for detecting the process parameters of the fluid under test, and so forth.
The cell voltage measurement unit 8 takes measurements on the output voltage of the thionyl chloride based primary cell 1, and an output of the cell voltage measurement unit 8 is connected to the connection controller 3. The communication unit 5 receives a communication signal EXT from outside, and an output thereof is connected to the connection controller 3.
The control operation unit 4 is connected to the first circuit block 7a, the second circuit block 7b, and the connection controller 3, thereby transmitting and receiving data such as measured values, and so forth, and a control signal. Further, the control operation unit 4 receives a process signal detected by the sensor of the second circuit block 7b, and calculates the measured value (a process value) on the basis of the process signal, outputting the measured value to the first circuit block 7a to be thereby displayed.
With the thionyl chloride based primary cell 1, and the internal circuit 9, constituted as described above, the internal circuit 9 is driven upon receiving supply of a discharge current from the thionyl chloride based primary cell 1, the discharge current serving as a power source current.
Now, in the case of the communication unit 5 carrying out radio communication via an antenna AT, the thionyl chloride based primary cell 1 large in power capacity, and small in self-discharge is employed as the power source of the measuring system 10 provided with a radio communication function. Further, for the thionyl chloride based primary cell 1 wherein thionyl chloride is used as solvent, use is made of, for example, a lithium thionyl chloride primary cell.
The thionyl chloride based primary cell 1 has an advantage in that a chloride film is formed on the surface of an anode in view of its properties, and according to its preservation state, and so forth, thereby preventing self-discharge. On the other hand, internal resistance will increase due to the chloride film formed therein. In this case, if there occurs an increase in the discharge current, this will cause an increase in voltage drop due to internal resistance, thereby lowering an output voltage.
With the measuring system 10 provided with the radio communication function, employing the thionyl chloride based primary cell 1 as the power source of the system, when measurement or radio communication is not executed, the measuring system 10 is in a standby state where a consumed current (power source current) is small in order to check a decrease in the power capacity of the cell while the measuring system 10 is in a normal operation state where the consumed current (the power source current) is large when the measurement or the radio communication is executed.
In this connection, since the consumed current in the standby state is very small in value, and if the standby state lasts for a long duration, a chloride film is formed, continuing growth. In the case of an increase in internal resistance, due to growth of the chloride film, if the measuring system 10 shifts to the normal operation state, thereby causing the consumed current to increase, this will raise a possibility that the output voltage of the thionyl chloride based primary cell 1 will drop to thereby cause stoppage in operation of the internal circuit 9, or the internal circuit 9 will occasionally run away.
Furthermore, if use is made of the thionyl chloride based primary cell 1 that has been unused as yet, and preserved over a long term, thereby causing growth of the chloride film, and resulting in a large internal resistance, there can be cases where initial activation of the internal circuit 9 cannot be effected because of a drop in the output voltage of the thionyl chloride based primary cell 1 at the time of the initial activation.
Accordingly, in order to normally effect the operation, and the initial activation of the internal circuit 9, or to prevent the internal circuit 9 from running away, the discharge current is controlled as follows.
In a first control of the discharge current, the discharge current is increased in stages. Such an operation is described hereinafter.
In FIG. 6, first, the control operation unit 4 such as a processor and so forth is in the standby state before the communication unit 5 receives the communication signal EXT via the antenna AT. In the standby state, the consumed current of the control operation unit 4 is small in value, so that the discharge current of the thionyl chloride based primary cell 1 is also small in value (step A).
Subsequently, upon receiving the communication signal EXT, the communication unit 5 outputs an interrupt signal to the connection controller 3. The connection controller 3 outputs a state-control signal to the control operation unit 4, and the control operation unit 4 receives the state-control signal, whereupon the control operation unit 4 shifts from the standby state to the operation state.
In the operation state, as the consumed current of the control operation unit 4 increases, so does the discharge current as well. As a result of an increase in the discharge current, the voltage drop due to the internal resistance will increase, so that the output voltage of the thionyl chloride based primary cell 1 will abruptly drop (step B).
While the output voltage of the thionyl chloride based primary cell 1 abruptly drops, the chloride film is removed, or reduced due to an increase in the discharge current, thereby reducing the internal resistance, whereupon the output voltage is gradually restored. Accordingly, the connection controller 3 monitors the output voltage of the thionyl chloride based primary cell 1, measured by the cell voltage measurement unit 8, and waits until the output voltage is restored to a voltage sufficient to enable the internal circuit 9 to be driven.
After restoration of the voltage, the connection controller 3 outputs a connection control signal to the first connector 6a, and upon the first connector 6a receiving the connection control signal, the first connector 6a connects input/output thereof.
By so doing, the first circuit block 7a receives supply of the power source current from the constant voltage circuit unit 2 via the first connector 6a, so that the discharge current will increase. As a result of an increase in the discharge current, the output voltage of the thionyl chloride based primary cell 1 undergoes an abrupt drop (step C).
Then, the connection controller 3 waits until the output voltage of the thionyl chloride based primary cell 1 is restored. After restoration of the voltage, the connection controller 3 outputs a connection control signal to the second connector 6b, and upon the second connector 6b receiving the connection control signal, the second connector 6b connects input/output thereof.
By so doing, the second circuit block 7b receives supply of the power source current from the constant voltage circuit unit 2 via the second connector 6b, so that the discharge current will increase. As a result of an increase in the discharge current, the output voltage of the thionyl chloride based primary cell 1 undergoes an abrupt drop, and thereafter, the output voltage is restored (step D).
Thus, the internal circuit 9 has a plurality of states differing in the discharge current from the step to the step. And current is supplied in stages to the respective units {including the respective blocks (the same applies hereinafter)} of the internal circuit 9 to cause the discharge current to increase, thereby normally executing the operation and the initial activation of the internal circuit 9, or preventing the internal circuit 9 from running away. Similar control of the discharge current is described in Patent Document 1.
In a second control of the discharge current, a time length for causing the discharge current to flow is computed on the basis of an average consumed current of the internal circuit 9, and the chloride film is activated by causing the discharge current to flow during the time length, thereby normally executing the operation and the initial activation of the internal circuit 9, or preventing the internal circuit 9 from running away. Similar control of the discharge current is described in Patent Document 2 (in Patent Document 2, the time length for causing the discharge current to flow is defined as refresh time).
Further, in Patent Document 3, there is described a technology capable of checking whether a voltage drop detection signal of the thionyl chloride based primary cell 1 is attributable to insufficient removal of the chloride film, or to a drop in the cell voltage, thereby sending out accurate information on the drop in the cell voltage.
[Preceding Technical Literature]
    [Patent Document] JP 1993-176091A    [Patent Document] JP 1993-63837 A    [Patent Document] JP 1993-323000 A